The aim of the present study was to analyze the increased airway reactivity to antigen induced by β-adrenoceptor blockade, adrenalectomy or medullectomy and to assess the contribution of circulating catecholamines to the increased reactivity. In anesthetized guinea pigs sensitized to ovalbumin (OA), administration of OA produced a dose-related bronchoconstriction characterized by threshold increases in airway insufflation pressure at 0.1 mg/kg i.v. and a near-maximal increase by 0.3 mg/kg i.v. Pretreatment with R(+) propranolol (0.5 mg/kg i.v.) 5 min prior to antigen did not significantly alter airway responses to antigen when compared to vehicle-treated animals. However, pretreatment with 0.5 mg/ kg i.v. S(––) propranolol, racemic propranolol or nadolol markedly enhanced (10- to 15-fold) the airway response to the low-dose antigen. In addition, in guinea pigs which had been adrenalectomized, the reactivity to low-dose antigen was enhanced to a similar extent as that of β-antagonist-treated animals when compared to sham-operated animals. Baseline plasma concentrations of epinephrine were significantly higher in sham-operate guinea pigs (1,494±223 ng/ml) when compared to adrenalectomized animals (412±44 ng/ml). Upon antigen exposure, epinephrine levels rose 5-fold (6,859±1,308 ng/ml) from baseline in sham-operated guinea pigs and were not significantly changed in adrenalectomized animals (848+208 ng/ml). Specific airway conductance measurements in conscious guinea pigs revealed that animals which had been medullectomized 2 weeks previously responded to lower provocative concentrations of aerosol OA (0.05–0.5%) than corresponding sham-operated animals. Airway reactivity to inhaled acetylcholine (0.1–1%) was similar in medullectomized and sham guinea pigs. Plasma concentrations of epinephrine were significantly lower in medullectomized guinea pigs (327 ± 88 ng/ml) when compared to sham-operated animals (832±162 ng/ml). The results of the present study indicate that β-adrenoceptor antagonism or changes in circulating epinephrine levels markedly alter the response to antigen in sensitized guinea pigs.

The aim of this study was to measure the effects of food restriction on antigen–induced bronchoconstriction and inflammatory cell influx in guinea pigs and to determine the role of plasma cortisol and catecholamine concentrations. Ovalbumin (OA; 0.3 mg/kg, i.v.) was administered to OA–sensitized, anesthetized guinea pigs which had been allowed free access to food or had been food restricted for 18 h prior to OA challenge. In addition to higher plasma levels of epinephrine (30% increase) and cortisol (33% increase), fasted guinea pigs had significantly lower (60% decreased) maximal bronchoconstrictor responses to OA than nonfasted, sensitized litter mates. Additionally, groups of fasted or fed animals were subdivided into two additional treatment groups: (1) saline–pretreated or (2) polyethylene glycol 400 (PEG)–pretreated (1 ml/kg, p.o., 1 h prior to antigen challenge). In saline–treated, fasted animals, bronchoconstrictor responses to antigen were significantly diminished (67% decreased) and epinephrine and cortisol levels were increased (64 and 34%, respectively) compared to the corresponding fed group. In both fasted and fed groups, the PEG–treated guinea pigs had higher plasma epinephrine and cortisol levels than animals which received saline, but no significant differences were detected within the PEG–treated group. Plasma norepinephrine concentrations were lower in all fasted groups. In a separate model in conscious guinea pigs, there were no differences in aerosol OA–induced bronchoconstriction and eosinophil influx between fasted and fed groups. However, compared to the saline pretreatment group, PEG administration reduced the antigen–induced bronchoconstriction and eosinophilia in both fed and fasted guinea pigs. We speculate that the reduced responsiveness to antigen in fasted versus fed animals may result from food–restriction–induced, stress–related release of epinephrine and cortisol from the adrenal glands, thereby suppressing mast cell degranulation or reducing responsiveness to spasmogenic and chemotactic mediators. In addition, the results suggest that oral dosing with 100% PEG may enhance this phenomenon.